The present invention relates to a hypoid ring gear for FR (front engine rear drive) vehicle differentials and a method of producing the same.
This type of hypoid ring gear for differentials (hereinafter referred to as the hypoid ring gear) has heretofore been produced, as shown in FIG. 6, by heating a round rod blank A1, upset-forging it to form a first disk-like intermediate article A2, die-forging said first intermediate article A2 to form a second intermediate article A3 in the form of a bottom-closed annular body having substantially the same inner and outer diameters as the end product, punching out the bottom A3xe2x80x2 of said second intermediate article A3 to form a third intermediate article A4 in the form of a bottom-opened annular body, normalizing and shot-blasting said third intermediate article A4, lathing said third intermediate article A4 as by an NC lathe to form a fourth intermediate article A5 in the form of a crude product, roughly gear-cutting said fourth intermediate article A5 on a Gleason gear cutting machine for rough machining, and finish-gear-cutting it on a Gleason gear cutting machine for finish machining, thereby providing an end product A6 having hypoid teeth g cut therein.
Since the conventional method of producing hypoid ring gears includes the step of directly die-forging the first disk-like intermediate article A2 to form said second intermediate article A3 in the form of a bottom-closed annular body having substantially the same inner and outer diameters as the end product A6, it needs a large-sized forge press. Besides this, it has to use two expensive Gleason gear cutting machines for cutting hypoid teeth g, thus presenting the drawback of the installation cost being very high. Further, since hypoid teeth g are formed by cutting, there are drawbacks in that the allowance for cutting (the amount to be lathed and the amount to be cut for tooth formation) increases, thus not only decreasing the yield of material but also prolonging the cutting time, thereby increasing the running cost.
Further, a hypoid ring gear produced by the conventional method has its hypoid teeth g formed by cutting, with the result that the flow of metal in the hypoid teeth g has been cut away by the cutter, thus decreasing the tooth surface strength. Therefore, a larger hypoid ring gear is required for transmission of a heavier load, thus presenting the drawback that the differential has to be increased in size.
The present invention has been proposed with the above drawback in the prior art in mind, and its object is to provide a hypoid ring for differentials and a method of producing the same, which are capable of reducing the installation cost and the running cost, minimizing the production cost and improving the tooth surface strength of the hypoid gear.
To achieve said object, the invention provides a method of producing hypoid ring gears for differentials, comprising the steps of upset-forging a round bar blank heated to a predetermined temperature to form a first disk-like intermediate article, die-forging said first intermediate article to form a second intermediate article in the form of a bottom-closed annular body which is smaller in inner and outer diameters and larger in axial thickness than the end product, punching out the bottom of said second intermediate article to form a third intermediate article in the form of a bottom-opened annular body which is smaller in inner and outer diameters and larger in axial thickness than the end product, shot-blasting said third intermediate article to remove the scale and then reheating it to a predetermined temperature and ring-rolling it to form a fourth intermediate article in the form of a crude product which is somewhat smaller in inner and outer diameters and somewhat larger in axial thickness than the end product, orbitally forging said fourth intermediate article to form a fifth intermediate article having hypoid teeth formed therein by orbital forging, normalizing and shot-blasting said fifth intermediate article to effect normalization and scale removal, punching out the internal burr formed on said fifth intermediate article during tooth forming operation based on orbital forging, and cold-coining it to form an end product.